Shell molding



United States Patent SHELL MOLDING Philip R. White, Detroit, Mich,assignor to General Motors Corporation, Detroit, Mich, a corporation ofDelaware No Drawing. Application February 4, 1952, Serial No. 269,909

3 Claims. (Cl. 22-193) This application has to do generally with patternequipment as used in foundry operations for forming metal castings andis more particularly concerned with improved metal pattern equipment.

There are several processes which have been proposed for use in formingmolds for foundry operations in which very accurate and smooth surfacefinishes are required. For example, one process sometimes calledsand-resin or shell molding is in use in which a dry mixture of sand andthermosett-ing resin binder is applied to a metal pattern heated to atemperature of about 250 to 350 F. or higher. After a short timeinterval the resin in the sandresin mix becomes molten and serves tobind the adjacent sand grains together to form a shell mold. The excesssand-resin mixture is then removed and the heated metal pattern with anadhering layer of the sand-resin mixture is heated to a highertemperature to set or cure the thermosetting binder and form arelatively strong thin-walled mold. The shell mold then is stripped fromthe metal pattern. Phenolformaldehyde and melamine formaldehyde resinsare typical examples of the resins employed.

In another process a mixture of a binder and silica flour is sprayed ona heated metal pattern. In this procedure the first coating of silicaflour and binder is coated with a sealing coat and thereafter a secondcoat of a mixture similar to the first is sprayed onto the sealing coat.The metal pattern with the sprayed coatings then is heated to set thebinder which may be sodium silicate. The layers on the metal pattern arethen backed up with refractory sand and binder. After heating to set thebinder the mold is removed from the pattern. In both of the foregoingdescribed processes the pattern equipment must be of metal because ofthe temperatures which are employed which would damage patterns ofnon-metallic materials.

In those processes in which metal patterns are used it has been commonpractice to form them of various materials such as cast iron, bronze,brass, aluminum and aluminum base alloys. Aluminum and the aluminum basealloys are particularly advantageous because of their heat conductingcharacteristics and because of the fact that they are relatively lightin weight. However, aluminum and aluminum base alloy patterns have thedisadvantage that as normally used they are more susceptible toscratching, abrasion and surface wear than are ferrous metals, brass orcopper, etc. Accordingly, the primary object of this invention is toimprove aluminum and aluminum base alloy patterns for use in makingmolds for foundry operations generally and especially for use in foundryoperations in which the patterns are heated during the formation of themolds.

Other objects and advantages of the present invention will become moreapparent as the description proceeds.

In accordance with the present invention the objects are attained byform-ing an anodized layer on the surface of aluminum or aluminum basealloy pat-terns. By aluminum base alloys is meant those alloys ofaluminum which contain about 80% or more of aluminum. Any of the knownprocesses for anodizing aluminum may be employed to provide the anodizedcoating or surface on the patterns in accordance with the presentinvention. Preferably the anodizing treatment is carried out to thepoint where there is an anodized coating on 'the aluminum or aluminumbase alloy pattern having a thickness of .0001 to .0002 inch. As atypical example of one anodizing solutionwhich has been found especiallysuitable, reference is made to an aqueous solution containing by volume20% sulfuric acid and 5% oxalic acid. The metal pattern is made theanode in'the solution. A voltage of 12 to 20 volts D. C. is employed. Atemperature of F. has been found especially suitable for this anodizingsolution. An anodizing time of 30 minutes in the described solution hasproduced an anodized coating which has been found quite satisfactory.

Prior to anodizing the pattern it is highly desirable to thoroughlyclean the same. Where the pattern may have organic material thereon itis removed from the pattern and thereafter the pattern is given a lightvapor blast. After the vapor blast treatment the pattern may be dippedin a conventional alkaline cleaner for approximately 10 seconds.Thereafter the pattern is rinsed in water and is then ready for theanodizing treatment. After the anodizing treatment the pattern is rinsedwith water and then dried.

In the formation of molds by use of heated metal patterns it is commonpractice to apply a mold release agent to the metal pattern. Manymaterials have been proposed for this purpose. However, best resultshave been obtained by use of mold releasing agents which containcarnauba wax or similar natural waxes. These waxes aid greatly inreleasing the mold from the heated metal pattern. Usually the Wax isapplied to the heated pattern in a mixture or solution of the wax and aliquid vehicle. Any of the materials and procedures described in thecopending application Serial No. 237,825, Mold Release Agents forSand-Resin Molds, filed July 20, 1951, in the name of Donald J. Henryand assigned to the assignee of the present application, may beemployed. Other mold release agents which have been employed comprisevarious silicone type materials. The molds formed by use of theanodizied aluminum or aluminum base alloy patterns in accordance withthe present invention increase the pattern life by retaining the smoothsurface finish, accurate dimensions and intricate pattern details. Theanodized layer of the .0001 to .0002 inch in thickness does not impairthe desirable thermal properties of the aluminum or aluminum alloypatterns. At the same time the patterns are highly scratch and wearresistant. In addition, the anodized aluminum or aluminum base alloypatterns in accordance with the present invention show easier release ofthe sand-resin or other molds when using carnauba wax lubricant or moldrelease agent than conventional aluminum patterns operating undersimilar conditions.

Where it may be necessary to remove periodically the carnauba waxlubricant residue resulting from continued pat-tern usage it may beremoved from the metal pattern by heating the same in a circulatingair-type furnace for 1 to 2 hours at 820 F. without in any way harm-ingthe wear-resistant anodized layer. In the appended claims the wordaluminum is intended to include not only pure or commercially purealuminum but also the aluminum base alloys containing about 80% or morealuminum. It will be understood that the term pattern as used in theclaims includes both mold patterns and core boxes and that the term moldincludes both molds and cores.

Various changes and modifications may be made in the specificembodiments of my invention described herein without departing from theprinciples and spirit of the invention.

I claim:

1. The method of forming a mold for use in metal casting operationswhich comprises making an aluminum metal pattern, forming an anodizedsurface layer on said aluminum pattern having a thickness of .0001 to.0002 inch, applying a mold release agent consisting essentially ofcarnauba wax to the anodized surface of said aluminum pattern, heatingsaid aluminum metal pattern as thus treated and applying a mold formingmaterial comp-rising nonmetallic refractory material and a heathardenable binder to said heated metal pattern.

2. The method of making a mold consisting essentially of nonmetallicrefractory material and a heat hardenable binder which comprisesapplying a mixture of said nonmetallic refractory material and heathardenable binder to a heated aluminum pattern having an anodizedsurface layer of about .0001 to .0002 inch in thickness and 15 carnaubawax on said anodized layer.

3. The method of making a mold consisting essentially of nonm'etallicrefractory material and a heat hardenable binder which comprisesapplying a mixture of said nonmetallic refractory material and heathardenable binder to an aluminum pattern heated to a temperature on theorder of 250-350 F. having an anodized surface layer of about .0001 to.0002 inch in thickness and carnauba wax on said anodized layer.

References Cited in the file of this patent UNITED STATES PATENTS840,251 Pinkus Jan. 1, 1907 1,965,682 Work July 10, 1934 2,023,645Newton et a1 Dec. 10, 1935 2,056,048 Gregory Sept. 29, 1936 2,294,717Carney Sept. 1, 1942 FOREIGN PATENTS 543,577 Great Britain Mar. 4, 1942OTHER REFERENCES Anodic Coating of Aluminum, by Edwards. Pub. June 1939.Entire Booklet has 22 pages. Page 16 relied upon.

Metal Industry, Nov. 10, 1944. Pages 290-293, inclusive.

Modern Metals, October 1950, pages 22-24.

2. THE METHOD OF MAKING A MOLD CONSISTING ESSENTIALLY OF NONMETALLICREFRACTORY MATERIAL AND A HEAT HARDENABLE BINDER WHICH COMPRISESAPPLYING A MIXTURE OF SAID NONMETALLIC REFRACTORY MATERIAL AND HEARHARDENABLE BINDER TO A HEATED ALUMINUM PATTERN HAVING AN ANODIZEDSURFACE LAYER OF ABOUT .0001 TO .0002 INCH IN THICKNESS AND CARNAUBA WAXON SAID ANODIZED LAYER.